+1 on Berkey + Soda Stream
If you drink a ton of bubbly you can hook up to a larger CO2 tank and fill them up at a home brew store.
Here’s a blog that convinced me to go that route:
https://www.frugalwoods.com/2014/08/11/how-to-cheap-homemade-seltzer-with-a-modified-sodastream/
